Many prior art attempts to tailor compressor and evaporator capacity to the cooling and dehumidification requirements of an air conditioned space have consisted of systems where parallel separate circuits contained essentially duplicate systems of compressors, evaporators, condensers, and other auxiliary equipment. In some cases, dehumidification has been achieved by using the full capacity of an evaporator while operating with more compressor capacity than is used in normal comfort cooling operation with the full capacity of the evaporator, which results in a portion of the compressor capacity which is used only in the dehumidification phase of the operation. At least one commercial available air conditioner, Yorkaire conditioners Models 351 and 551, manufactured by the York Corporation, York, Pennsylvania, in 1950, was equipped with a valve which cut off the refrigerant from half the evaporator coils so that the entire compressor output was concentrated in the other half of the evaporator coil and thereby cooled the evaporator sufficiently for dehumidification. However, it is reported that this evaporator operated at such a low temperature that the evaporators were constantly freezing up solid because their surface temperature dropped below 32.degree. F.
U.S. Pat. No. 4,018,584 discloses three embodiments which appear to capsule the prior art. The first embodiment, as best shown in FIG. 2, comprises two compressors, at least one of them a multi-capacity compressor, in separate, but generally parallel refrigerant circuits, providing for both cycling and continuous operation of each compressor, and for high and low capacity operation of the multi-capacity compressor, but always in conjunction with the full capacity of the refrigerant evaporator associated with the operative compressor. This embodiment provides for various operating modes depending upon conditions sensed in the conditioned space, such as full capacity operation of the multi-capacity compressor circuit for dehumidifying, low capacity compressor operation in the multi-capacity compressor circuit plus continuous operation of the other compressor circuit for maximum comfort cooling without dehumidification, and cycling of one or both of the compressors in comfort cooling mode for lesser comfort cooling capacity.
A second embodiment disclosed in U.S. Pat. No. 4,018,584 at column 5, lines 18-30, includes a two speed compressor in a refrigerant circuit utilizing the complete capacity of its evaporator to provide dehumidification or comfort cooling depending on whether the compressor runs at its high or low speed respectively. A third embodiment disclosed at column 5, lines 31-36, provides a fixed capacity compressor and an evaporator therewith which is appropriately valved for operation at full capacity for comfort cooling and for operation at a suitable portion of capacity to provide a colder evaporator and dehumidification thereby.
None of the above embodiments, however, provides the flexibility and adaptability inherent in the system of the present invention, where two compressors in parallel may be used with the entire capacity of the evaporator for maximum comfort cooling, either of the compressors may be used with a corresponding portion of the capacity of the evaporator for a reduced comfort cooling capacity, and both compressors may be used at full capacity with a suitably somewhat reduced portion of the evaporator capacity for dehumidification substantially without evaporator frosting.
The flexibility and adaptability of the present invention are particularly important in connection with the air conditioning and dehumidification of supermarkets, where a variety of refrigeration units, such as deep freeze units, meat display cabinets, and dairy product cases, each have cooling coils which are subject to frosting up from the ambient air moisture content and must be defrosted with regularity. These cooling coils also may lower the temperature of the supermarket to an uncomfortable point for the customers, particularly when the air conditioning system is used for dehumidification in spring and fall when cooling of the air may not be required otherwise, thus requiring that the air supplied be heated at times. Dehumdification of the supermarket atmosphere on a controlled basis provides significant savings in auxiliary heat required to defrost the various freezer and refrigerator cooling coils, as well as preventing condensation or frosting around the openings thereto, and promoting more efficient operation of the freezer and refrigerator cooling coils by minimizing the amount of front on their coils. Frost on the coils interferes with their cooling capacity, particularly where the coils must be maintained far below the freezing point of water, as in deep freeze cases. In the present system, otherwise waste heat which must be removed from compressed refrigerant before evaporation for cooling, may be used to reheat the treated air after dehumidification.
U.S. Pat. Nos. 3,596,474, 2,522,090, 4,003,729, and 3,703,814 provide other background for this invention. (Copies of the just-listed U.S. Patents and U.S. Pat. No. 4,018,584 plus a copy of Yorkaire Conditioners Models 351 and 551 Service Manual Instruction 11-0-5 are enclosed herewith.)